(1) Field of the Invention
This invention relates to the use of attenuating phase shifting masks and more particularly to rim type attenuating phase shifting masks used to avoid the problems of side-lobe effect.
(2) Description of the Prior Art
Phase shifting masks and attenuating phase shifting masks have been used in the manufacture of integrated circuit wafers for some time.
U.S. Pat. No. 5,593,801 to Yoshioka et al. describes an attenuating type phase shifting mask used with an attenuating auxiliary type phase shifting mask and their use in the manufacture in integrated circuit wafers.
U.S. Pat. No. 5,288,569 to Lin describes the use of feature biassing applied to phase shifting masks to improve the exposure latitude and depth of focus of an optical projection imaging system.
U.S. Pat. No. 5,510,214 to Pan et al. describes the use of a double destruction phase shifting mask which combines transparent phase shifting regions and attenuating phase shifting regions to improve the quality of images produced by the masks.
The mask and methods described herein are different from the inventions of Yoshioka et al., Lin, or Pan et al. In the present invention a mask having a first pattern formed in attenuating phase shifting material is used with a second pattern formed in opaque material to form a rim type mask. The pattern edge is defined by the first pattern in the attenuating phase shifting material thereby achieving the advantages of an attenuating phase shifting mask. The rim formed from the pattern in the opaque material prevents problems resulting from the side-lobe effect due to the light transmitted through the attenuating phase shifting material.